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Kai Ryssdal: Yet another study out today confirmed girls are reaching puberty earlier -- way earlier, like around seven or eight. Aside from the minefield of social dilemmas these kids may have to sidestep, early development like that is linked to obesity. And over time, medical issues linked to obesity hit national health care costs on the order of billions of dollars.

Janet Babin reports now from North Carolina Public Radio.

Janet Babin: Researchers don't know precisely what's behind early onset puberty, but they have an idea.

Dr. Susan Pinney at the University of Cincinnati College of Medicine was one of the study's investigators. She says early puberty is tied to the growing epidemic of obesity in children.

Susan Pinney: Our analyses showed that as a group, girls who were obese definitely tended to enter puberty earlier.

That's dangerous to the girl's health and to the national economy. Justin Trogdon is an economist at research institute RTI International. He says people who suffer from obesity spend an average of $1,400 more each year on health care than people who are not as overweight.

Justin Trogdon: It works out to about $147 billion per year.

Most of those increased costs pay for treatment of high blood pressure and high cholesterol. And obesity raises the risk of heart disease and cancer.

Trogdon: If children are developing obesity earlier, it makes it all that more likely that they'll develop those kinds of conditions, like diabetes, and heart disease and potentially cancers at an earlier age, and that can impact costs for the entire nation as we look forward.

The study's authors also documented more than 100 different chemicals in the girls' blood, and expect to publish those results shortly. The Breast Cancer and the Environment Research Centers helped pay for the study, published in the journal Pediatrics.